1. Field of the Invention
The present invention relates to an electrostatic drive type ink-jet head. More particularly, the invention relates to an ink-jet head which is compact, requires reduced number of parts and easy to produce. Further particularly, the invention relates to an ink-jet printer mounting the ink-jet head.
2. Description of Related Art
As is well known, the electrostatic drive type ink-jet head is constructed to vary a volume of an ink pressure chamber communicated with an ink ejection nozzle by an electrostatic force and to eject a predetermined shape of ink droplet from the ink ejection nozzle utilizing a pressure variation generated in the ink pressure chamber. This type of the ink-jet head has been disclosed, for example, in U.S. Pat. No. 5,513,431 issued on May 7, 1996 and assigned to the same assignee of the present application.
Generally known electrostatic drive type ink-jet head has a plurality of ink pressure chambers respectively communicated with a plurality of ink ejection nozzles arranged in alignment. For avoiding influence of pressure variation in each ink pressure chamber to other ink pressure chamber, each ink pressure chamber is connected to a common ink chamber having large capacity, via an ink supply orifice. The common ink chamber is formed with an ink supply port. To the common ink chamber, an ink is supplied from an ink source through the ink supply port.
As disclosed in the above-identified U.S. Patent, at backside position of the ink ejection nozzles arranged in alignment, the ink pressure chambers are arranged in plane direction. On the backside position of these ink pressure chambers, ink supply orifices extending toward backside of the ink-jet head are formed. On backside position of these ink supply orifices, the common ink chamber is arranged on the same plane direction. The ink supplied to the common ink chamber through the ink supply port flows toward front side of the ink-jet head on the plane direction and is supplied to each ink pressure chamber through the ink supply orifice from the front end portion of the common ink chamber.
On the other hand, the electrostatic drive type ink-jet head of the construction set forth above is typically constructed with a semiconductor substrate. For example, by providing anisotropic wet etching for the surface of the monocrystalline silicon substrate, a groove for the common ink chamber and grooves for the ink pressure chambers are formed. Normally, by providing anisotropic wet etching from the surface of the monocrystalline silicon substrate having crystal orientation face of (100), a predetermined depth of rectangular groove in plane shape is formed, for example, for the common ink chamber.
Here, in the conventional electrostatic drive type ink-jet head, the ink pressure chambers, ink supply orifices and the common ink chamber are arranged on the common plane along a longitudinal direction of the ink-jet head. Accordingly, the ink-jet head is elongated in the longitudinal direction.
Therefore, for example, as disclosed in U.S. Pat. No. 5,963,234 issued on Oct. 5, 1999 and assigned to the same assignee of the present application, it is considered to arrange the ink pressure chambers at a height position different from the plane where the ink pressure chambers are arranged. The ink-jet head disclosed in the above-identified publication is a piezoelectric drive type. The construction as it is, is not applicable for the electrostatic drive type ink-jet head. Also, in the ink-jet head disclosed in the above-identified U.S. Patent, the common ink chamber, the ink pressure chambers and the ink supply orifices are defined by stacking a plurality of substrates. Although such a construction permits shortening of length in the longitudinal direction, a dimension in the thickness direction is significantly increased. Also, the number of components becomes large and that of fabrication steps also becomes large.
On the other hand, in the conventional electrostatic drive type ink-jet head formed with the common ink chamber having a rectangular shape in plane view, the inner side wall of the common ink chamber where the ink supply orifices are communicated to the chamber, extends in a width direction of the ink-jet head, and thus extends substantially perpendicular to the ink supply orifices extending in the longitudinal direction of the ink-jet head. Accordingly, on the inner side surface of the common ink chamber, particularly on both corner portions thereof, ink stagnation can be formed. Therefore, bubble penetrating within the common ink chamber as mixed with the ink can be accumulated in the corner portions. Once bubble is accumulated in the corner portions of the common ink chamber, it becomes difficult to stably supply the ink to the ink pressure chambers via the ink supply orifices located in the vicinity of the corner portions.
If sufficient ink supply is not performed to the ink pressure chambers located at both ends, ejection of the ink droplet in an appropriate condition cannot be performed through the ink ejection nozzles communicated with such ink pressure chambers. If such failure is caused, degradation of printing quality can be caused due to fluctuation of the ink ejection characteristics of the respective ink ejection nozzles.
An object of the present invention is to provide an electrostatic drive type ink-jet head which can shorten a length in the longitudinal direction thereof.
Another object of the present invention is to provide an electrostatic drive type ink-jet head which has a smaller number of components, is easy to product and short in the longitudinal direction.
A further object of the present invention is to provide a short electrostatic drive type ink-jet head, which can prevent accumulation of bubble in the common ink chamber resulting in fluctuation of ink ejection characteristics among the ink ejection nozzles, and which can prevent lowering of ink ejection characteristics of the ink ejection nozzle on both end sides.
A still further object of the present invention is to provide an ink-jet printer having the novel ink-jet head.
In order to accomplish the above and other objects, an ink-jet head comprises:
a plurality of ink ejection nozzles;
a plurality of ink pressure chambers provided corresponding to the respective ink ejection nozzles and respectively communicated with the corresponding ink ejection nozzles;
a common ink chamber for supplying an ink to the respective ink pressure chambers;
a plurality of ink supply orifices provided corresponding to the respective ink pressure chambers and communicating the ink pressure chambers to the common ink chamber;
electrostatic actuators for varying volume of the respective ink pressure chambers by an electrostatic force for ejection of ink droplets from the corresponding ink ejection nozzles,
a plurality of the ink pressure chambers being arranged in a plane; and
the common ink chamber being stacked on the plurality of ink pressure chambers.
The ink-jet head according to the present invention can reduced the length thereof for the reason that the common ink chamber is stacked on the ink pressure chambers.
In the typical example, the ink-jet head includes a first substrate, a second substrate stacked on an upper surface of the first substrate and a third substrate stacked on an upper surface of the second substrate,
the third substrate being formed with the common ink chamber and the ink supply orifices;
the second substrate being formed with the ink pressure chambers communicated with the ink ejection nozzles; and
the electrostatic actuators being disposed between the first substrate and the second substrate.
In the three-layered structure, the nozzle grooves for forming the ink ejection nozzles are formed on a lower surface of the third substrate opposing the second substrate, on an upper surface of the second substrate, grooves for forming the ink pressure chambers are formed.
Instead of forming the nozzle grooves for forming the ink ejection nozzles in the third substrate, the ink-jet head may further comprise a fourth substrate formed with the ink ejection nozzles, wherein ink communication holes communicated with the ink pressure chambers are exposed on front end faces of the stacked second and third substrates, and the fourth substrate is fitted on the front end faces so that the respective ink nozzles are communicated with the corresponding ink communication holes.
The common ink chamber may be defined by a groove for forming the common ink chamber formed on the upper surface of the third substrate and a film sealing the groove, and at least one ink supply orifice is formed through bottom portion of the groove for forming the common ink chamber. In comparison with the case of forming the thin grooves on the surface of the substrate, forming through holes in the bottom portion of the common ink chamber for forming the ink supply orifices is easier. Also, a plurality of the ink supply orifices can be formed relatively easily. Furthermore, freedom in the designing the section and dimension of the orifice can be increased to facilitate adjustment of flow resistance of the ink supply orifice and thus to facilitate adjustment of the ink ejection characteristics of the ink-jet head. By forming greater number of ink supply orifices, if one of the orifices is blocked by a foreign matter contained in the ink, significant increase of ink flow resistance will be avoided, whereby maintaining a continuous ink supply to avoid harmful affect on the ink ejection amount, ink ejection speed and so forth.
In order to fabricate the third substrate having the nozzle grooves for forming the ink ejection nozzles, the ink supply orifices and the common ink chamber, the third substrate is a monocrystalline silicon substrate, the nozzle grooves for forming the ink ejection nozzles and the ink supply orifices are formed by trench etching by an ICP (inductively coupled plasma) discharge, and the groove for forming the common ink chamber is formed by anisotropic wet etching.
The film may be formed with the ink supply port, and a rib for supporting the film is provided in the common ink chamber for preventing the portion of the film where the ink supply port is formed, from deflecting in out-of-plane direction.
The ink-jet head may further comprise an ink supply port for introducing an ink into the common ink chamber, the ink supply orifices are communicated with a first end portion of the common ink chamber and the ink supply port is communicated with a second end portion of the common ink chamber, and a shape of the common ink chamber in plan view is tapered to be widen from the second end portion to the first end portion.
With this shape of the common ink chamber, the ink introduced into the common ink chamber through the ink supply ports can quickly flow toward the ink supply orifices in the common ink chamber without stagnation therein. Accordingly, accumulation of bubble in the common ink chamber due to stagnation of the ink therein can be successfully prevented or restricted. Particularly, stagnation of the ink at the corner portion of the common ink chamber at both end portions in the lateral or width direction can be prevented or restricted.
In the typical construction, the first end may be an end of the common ink chamber located at rear end side of the ink-jet head and the second end is an end of the common ink chamber located at front end side of the ink-jet head.
A bottom portion and inner peripheral side wall of the common ink chamber may be defined by a groove formed by anisotropic wet etching of a monocrystalline silicon substrate for a predetermined depth, and crystal orientation of the monocrystalline silicon substrate is (100), and the groove is defined by inner peripheral side walls having respective orientations parallel to (011) orientation face, 45xc2x0 to the (011) operation face, and 90xc2x0 to the (011) orientation face.
Particularly, it is desirable that the groove is defined by inner peripheral side walls having respective orientations parallel to (011) orientation face, 19xc2x0 to the (011) operation face, 45xc2x0 to the (011) operation face, and 90xc2x0 to the (011) orientation face.
By performing an isotropic wet etching, the respective inner peripheral side walls of the common ink chamber can easily be formed to be flat surfaces, flow of the ink in the common ink chamber becomes smooth to contribute for restriction or elimination of stagnation of bubble therein.
The electrostatic actuator may include a vibration plate formed in a bottom portion of each of the ink pressure chamber, elastically displaceable in out-of-plane direction and serving as a common electrode, and an individual electrode formed on the upper surface of the first substrate and opposing to the vibration plate with a given clearance therebetween.
According to another aspect of the present invention, an ink-jet printer comprises:
an ink-jet head as set forth above;
a printing paper feeding mechanism for feeding a printing paper across a printing position where printing is performed by the ink-jet head; and
drive control means for driving the ink-jet head for performing printing on the printing paper passing across the printing position.
The ink-jet head is a line ink-jet head with the ink ejection nozzles arranged over an entire printing width. In the alternative, the ink-jet printer may be one that comprises a carriage carrying the ink-jet head for reciprocal motion over a printing width.